| Type |
Journal Article |
| Names |
Amanda A. Kepley, Stefanie Mühle, John Everett, Ellen G. Zweibel, Eric M. Wilcots, Uli Klein |
| Publication |
The Astrophysical Journal |
| Volume |
712 |
| Issue |
1 |
| Pages |
536-557 |
| Date |
March 1, 2010 |
| URL |
http://adsabs.harvard.edu/abs/2010ApJ...712..536K |
| Library Catalog |
NASA ADS |
| Abstract |
NGC 1569 is a nearby dwarf irregular galaxy which underwent an intense
burst of star formation 10-40 Myr ago. We present observations that
reach surface brightnesses 2-80 times fainter than previous radio
continuum observations and the first radio continuum polarization
observations of this galaxy at 20 cm, 13 cm, 6 cm, and 3 cm. These
observations allow us to probe the relationship of the magnetic field of
NGC 1569 to the rest of its interstellar medium (ISM). We confirm the
presence of an extended radio continuum halo at 20 cm and see for the
first time the radio continuum feature associated with the western
Hα arm at wavelengths shorter than 20 cm. Although, in general,
the spectral indices derived for this galaxy steepen as one moves into
the halo of the galaxy, there are filamentary regions of flat spectral
indices extending to the edge of the galaxy. The spectral index trends
in this galaxy support the theory that there is a convective wind at
work in this galaxy. There is strong polarized emission at 3 cm and 6 cm
and weak polarized emission at 20 cm and 13 cm. We estimate that the
thermal fraction is 40%-50% in the center of the galaxy and falls off
rapidly with height above the disk. Using this estimate, we derive a
total magnetic field strength of 38 μG in the central regions and
10-15 μG in the halo. The magnetic field is largely random in the
center of the galaxy; the uniform field is ~3-9 μG and is strongest
in the halo. Using our total magnetic field strength estimates and the
results of previous observations of NGC 1569, we find that the magnetic
pressure is the same order of magnitude but, in general, a factor of a
few less than the other components of the ISM in this galaxy. The
uniform magnetic field in NGC 1569 is closely associated with the
Hα bubbles and filaments. We suggest that a supernova-driven
dynamo may be operating in this galaxy. Based on our pressure estimates
and the morphology of the magnetic field, the outflow of hot gas from
NGC 1569 is clearly shaping the magnetic field, but the magnetic field
in turn may be aiding the outflow by channeling gas out of the disk of
the galaxy. Dwarf galaxies with extended radio continuum halos like that
of NGC 1569 may play an important role in magnetizing the intergalactic
medium. |
| Tags |
Galaxies: ISM, galaxies: individual: NGC 1569, galaxies: irregular, galaxies: magnetic fields, galaxies: starburst, radio continuum: galaxies |